Quarterly report pursuant to Section 13 or 15(d)

Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details)

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Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details) - USD ($)
$ in Millions
Nov. 30, 2022
May 31, 2022
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses $ (92.7) $ (116.2)
Securities in an unrealized loss position for less than twelve months, Fair value 1,782.7 2,059.6
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (126.6) (22.8)
Securities in an unrealized loss position for more than twelve months, Fair value 827.4 200.7
Total, Gross unrealized losses (219.3) (139.0)
Total, Fair value 2,610.1 2,260.3
Asset-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses (0.8) (0.9)
Securities in an unrealized loss position for less than twelve months, Fair value 35.4 48.5
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (1.3) (0.3)
Securities in an unrealized loss position for more than twelve months, Fair value 14.1 5.7
Total, Gross unrealized losses (2.1) (1.2)
Total, Fair value 49.5 54.2
Corporate Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses (23.4) (17.5)
Securities in an unrealized loss position for less than twelve months, Fair value 584.0 425.4
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (12.8) (1.5)
Securities in an unrealized loss position for more than twelve months, Fair value 93.7 16.7
Total, Gross unrealized losses (36.2) (19.0)
Total, Fair value 677.7 442.1
Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses (38.6) (81.9)
Securities in an unrealized loss position for less than twelve months, Fair value 721.7 1,171.5
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (95.1) (10.6)
Securities in an unrealized loss position for more than twelve months, Fair value 606.5 86.6
Total, Gross unrealized losses (133.7) (92.5)
Total, Fair value 1,328.2 1,258.1
U.S. Government Agency And Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses (29.9) (15.9)
Securities in an unrealized loss position for less than twelve months, Fair value 441.6 414.2
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (17.4) (10.4)
Securities in an unrealized loss position for more than twelve months, Fair value 113.1 91.7
Total, Gross unrealized losses (47.3) (26.3)
Total, Fair value $ 554.7 $ 505.9